Kasumi Matsubara dedicates her life as a housewife to managing the household and caring for her daughter, Mio. Her routine expands to include her nephew, Ryoji, when he moves in, and she readily extends her nurturing care to him, accommodating his presence. She possesses distinctive purple eyes and auburn or brown hair, complemented by a light tan and a mole. Kasumi typically wears glasses, contributing to her reserved and gentle demeanor, fitting a conventional portrayal. Despite her composed exterior, Kasumi experiences significant emotional strain within her marriage. Feeling neglected by her husband, who provides financially but offers little attention or affection, she endures a prolonged absence of physical intimacy. Privately, she turns to masturbation to cope with these unmet needs, though it fails to ease her deeper isolation and dissatisfaction. This private coping leads to an incident where Ryoji inadvertently witnesses her during a moment of self-pleasure. This event becomes a turning point, preoccupying Ryoji and shifting their dynamic. He later walks in on her showering, fueling a persistent fixation. Ryoji becomes determined to address her perceived unmet needs, complicating the household stability. Family relationships anchor Kasumi's existence. She maintains a bond with her sister, Harumi, who later becomes involved in the situation with Ryoji. Her daughter, Mio, also develops her own connection to Ryoji, further intertwining their lives. Kasumi's generally passive nature surfaces during a home invasion, where she proves unable to defend herself effectively. Ryoji's intervention prevents greater harm, though a jewelry item is stolen. This incident reinforces her dependent role within the family structure.